1. Field of the Invention
The present invention pertains to compositions for inhibiting stress cracking in poly(alkylene terephthalate) articles of manufacture. More particularly, the present invention concerns aqueous-based fatty acid lubricant compositions containing such stress crack inhibitors. Even more particularly, the present invention concerns aqueous fatty acid-based lubricant concentrates and use solutions therefor which contain such stress crack inhibitors.
2. Prior Art
As is known to those skilled in the art to which the present invention pertains there has been an ever increasing usage of synthetic resinous containers for fluids and solids. Likewise, as is known to those skilled in the art, such containers are normally filled or washed by passing them through filling and capping stations or through a washing system along manually, mechanically or electronically-operated conveyor systems.
In order to ensure efficient operation of the filling or washing systems it is essential that the conveyor systems, per se, be continuously lubricated. Otherwise, the containers may stack up along the conveyor system and their movement could be impeded.
Thus, the conveyors are, ordinarily, continuously lubricated by applying to the conveyor a lubricant, such as by spraying or the like. Typically, conventional lubricants contain amines, alcohols and other constituents which have a deleterious effect on the poly(alkylene terephthalate) article disposed along the conveyor system.
Indeed, it has long been known that exposure by such articles to these lubricants leads to a phenomenon which has been identified as "stress cracking" and is especially prevalent in poly(alkylene terephthalate) containers and other such articles of manufacture. This is true with respect to both poly(ethylene terephthalate) and poly(butylene terephthalate) containers.
As noted, conventional aqueous-based lubricants containing alcohols and/or amines do not inhibit or prevent stress cracking in such containers, but rather, promote stress cracking.
In the copending application referred to above, there is disclosed a highly dilutable aqueous lubricant concentrate which appears to inhibit stress cracking by combining a tertiary alkyl amine as a saponifying agent, and an alkyl aryl sulfonate, as a solubilizing agent for a long chain fatty acid. While the compositions of the copending application are efficacious for preparing highly dilutable lubricants, it has now been found that the tertiary amine, per se, is not essential to the prevention of stress cracking, in poly(alkylene terephthalate) articles. Rather, it has now been found that a certain class of alkyl aryl sulfonates and other hydrophile-terminated aromatic compounds, when combined with free-base amines, will inhibit stress cracking when formulated into fatty acid lubricants. This finding enables the production of dilutable, cost efficient, fatty acid-based aqueous lubricant compositions without any dilatory effects caused by the presence of the amine. Likewise, this finding enables implementation of other means and methods for inhibiting stress cracking in poly(alkylene terephthalate) articles.
Heretofore, the only proposed method of inhibiting stress cracking in plastic bottles known to the applicants, has been the incorporation of an alkali metal salt of a hydrophilic substituted aromatic hydrocarbon and other hydrotropes into a liquid bleach, such as disclosed in EPA, EP No. 302705 AZ, filed Feb. 8, 1989. This application discloses the use of the hydrotropes as an adjustment to the bleach to inhibit stress cracking in high density polyethylene containers. Yet, the art has not directed itself to lubricants and other media for inhibiting stress cracking in polyethylene or polybutylene terephthalate bottles or other articles of manufacture.